We report on the realization of an open plane-concave Fabry-P\'erot resonator with a mode volume below λ3 at optical frequencies. We discuss some of the less common features of this new microcavity regime and show that the ultrasmall mode volume allows us to detect cavity resonance shifts induced by single nanoparticles even at quality factors as low as 100. Being based on low-reflectivity micromirrors fabricated on a silicon cantilever, our experimental arrangement provides broadband operation, tunability of the cavity resonance, lateral scanning and promise for optomechanical studies.
@article{arxiv.1502.02736,
title = {A Sub-$\rm \lambda^{3}$-Volume Cantilever-based Fabry-P\'erot Cavity},
author = {Hrishikesh Kelkar and Daqing Wang and Diego Martín-Cano and Björn Hoffmann and Silke Christiansen and Stephan Götzinger and Vahid Sandoghdar},
journal= {arXiv preprint arXiv:1502.02736},
year = {2015}
}